The footwear and leather industry among others requires reinforcing parts which must have a range of characteristics, the main characteristics being as follows:
they must be thermoformable at low temperature, in particular from 80.degree. C.-90.degree. C., and regain their rigidity fairly rapidly at ambient temperature; PA1 they must be thermoadhesive at low temperature, in particular from 80.degree. C.-90.degree. C., at a pressure of a few bars and in the space of a few seconds on a variety of backings such as natural or synthetic leathers, thermoplastic materials, natural or synthetic textiles, elastomers, etc.; and PA1 they must have low sensitivity to creep under normal conditions of use. PA1 the mixture is extruded under low shear conditions at a low temperature of 100.degree. C. to 140.degree. C. to produce a mixture with a paste-like consistency which is insufficient for the formation of a homogeneous mixture of molten polymers; PA1 following extrusion and optional addition of a textile backing to the extruded product, the product is rolled or calendered at high pressure at a temperature which is of the order of 100.degree. C. to reduce its thickness, with cooling to a temperature of less than 30.degree. C. before rolling or calendering is completed.
French patent FR-A-2 392 810 describes a product of this type constituted by a synthetic material (binder) reinforced with an inert filler material.
European patent EP-A-0 183 912 describes a material of the same type, in which the filler material is entirely or at least superficially constituted by plastics material.
In both cases the starting substances, the binder and the filler material, are constituted by powders with comparable grain sizes preferably of 50 .mu.m to 500 .mu.m, in particular 100 .mu.m to 400 .mu.m. Powders with such grain sizes can cause cost problems in production and handling as well as suffering from the usual problems of powders, namely static electricity and irregularity of the physico-chemical properties of the products obtained.
FR-A-2 559 503 describes stiffening materials for leather, constituted by at least one layer of synthetic material obtained by sintering a mixture of two polymer components with different melting points. The product obtained is not thermoadhesive.